The present invention relates to an improved in-ground/in-water heat exchange means for use in association with any heat pump heating/cooling system utilizing in-ground and/or in-water heat exchange elements as a primary or supplemental source of heat transfer, as well as to improved methods of installing in-ground and/or in-water heat exchange tubing.
Ground source/water source heat exchange systems typically utilize liquid-filled closed loops of tubing buried in the ground, or submerged in a body of water, so as to either absorb heat from, or to reject heat into, the naturally occurring geothermal mass and/or water surrounding the buried or submerged tubing.
Water-source heating/cooling systems typically circulate water, or water with anti-freeze, in plastic underground geothermal tubing so as to transfer heat to or from the ground, with a second heat exchange step utilizing a refrigerant to transfer heat to or from the water, and with a third heat exchange step utilizing a compressor and an electric fan to transfer heat to or from the refrigerant to heat or cool interior air space. Further, water-source heating/cooling systems typically utilize closed-loop or open-loop plastic tubing.
Closed-loop systems, often referred to as ground loop heat pumps, typically consist of a supply and return, xc2xe inch to 2 inch diameter, plastic tube, joined at the extreme ends via an elbow, or similar, connection. The plastic tubing is typically of equal diameter, wall thickness, and composition, in both the supply and return lines. The water is circulated within the plastic tubing by means of a water pump. In the summer, interior space heat is collected by an a commonly understood interior compressor and air heat exchanger system, or air handler, and is rejected and transferred into the water line via a refrigerant line to water line heat exchanger. In a similar manner in the winter, heat is extracted from the water line and transferred to the interior conditioned air space via the refrigerant liquid within the refrigerant line being circulated in a reverse direction. Many such systems are designed to operate with water temperatures ranges of about a 10 degree Fahrenheit (xe2x80x9cF.xe2x80x9d) water temperature differential between the water entering and exiting the heat exchange unit""s copper refrigerant transport tubing. Water temperatures are often designed to operate in the 40 to 60 degree F. range in the summer, and in the 25 to 45 degree F. range in the winter with anti-freeze added to the water. If a closed-loop, 1.5 inch diameter, plastic water conducting tubing is installed in a horizontal fashion about 5 or 6 feet deep, in 55 degree earth, about 200 to 300 linear feet per ton of system capacity may be necessarily excavated. If the same closed-loop plastic water conducting tubing is installed in a vertical borehole in 55 degree earth, about 150 to 200 feet per ton of system capacity may be necessarily drilled. Requisite distances are longer for horizontal systems because near-surface temperature fluctuations are greater. However, trenching costs are usually less than drilling expenses. In the horizontal style installation, the plastic tubing loop is typically backfilled with earth. In the vertical style installation, the plastic tubing loop inserted into the typical 5 to 6 inch diameter borehole is generally backfilled with a thermally conductive grout. In either the horizontal or the vertical style installation, a water pump is required to circulate the water through the tubing lines, which are generally of equal diameter in both the supply and return segments.
Open-loop systems, often referred to as ground water heat pumps, typically exchange heat to and from interior conditioned air in the same manner as a closed-loop system, but the water circulation segment differs. In an open-loop system, water is pumped from a supply source, such as a well, river, or lake, is run through the water to refrigerant heat exchanger, and is then rejected back into a well, river, or lake. While open-loop systems can significantly reduce plastic tubing excavation or drilling requirements on a system capacity tonnage basis, if an adequate water supply is available, these systems pose a potential environmental threat since bacteria in the surface water transport tubing can be transferred to, and can infect, the water which is being rejected back into the public water supply.
Direct Expansion (xe2x80x9cDXxe2x80x9d) ground source heat exchange systems typically circulate a refrigerant fluid, such as R-22, in copper underground or underwater geothermal tubing to transfer heat to or from the ground or water, and only require a secondary heat exchange step to transfer heat to or from the interior air space by means of an electric fan. In DX systems, the exterior heat exchange copper refrigerant tubing is placed directly in the geothermal soil and/or water. Historically, due to compressor operational limitations encountered with traditional DX designs installed at depths beyond 50 to 100 feet, most reverse-cycle DX systems, which operate in both the heating and the cooling modes, have been installed with an array of horizontal heat exchange tubes about 5 feet deep, or in vertical boreholes less than 100 feet deep. These prior limitations can be overcome via utilization of a supplemental refrigerant fluid pump, as disclosed in U.S. patent application Ser. No. 10/073,513, by Wiggs.
While most in-ground/in-water heat exchange designs are feasible, various improvements have been developed intended to enhance overall system operational efficiencies. Several such design improvements are taught in U.S. Pat. No. 5,623,986 to Wiggs, in U.S. Pat. No. 5,816,314 to Wiggs, et al., and in U.S. Pat. No. 5,946,928 to Wiggs, the disclosures of which are incorporated herein by reference. These designs basically teach the utilization of a spiraled fluid supply line subjected to naturally surrounding geothermal temperatures, with a fully insulated fluid return line, as well as improved subterranean heat transfer tubing and system component designs.
Other predecessor vertically oriented geothermal heat exchange designs are disclosed by U.S. Pat. No. 5,461,876 to Dressler, and by U.S. Pat. No. 4,741,388 to Kuriowa. Dressler""s ""876 patent teaches the utilization of an in-ground spiraled fluid supply line, but neglects to insulate the fluid return line, thereby subjecting the heat gained or lost by the circulating fluid to a xe2x80x9cshort-circuitingxe2x80x9d effect as the return line comes in close contact with the warmest or coldest portion of the supply line. Kuriowa""s preceding ""388 patent is virtually identical to Dressler""s subsequent claim, but better, because Kuriowa insulates a portion of the return line, via surrounding it with insulation, thereby reducing the xe2x80x9cshort-circuitingxe2x80x9d effect. Dressler""s ""876 patent also discloses the alternative use of a pair of concentric tubes, with one tube being within the core of the other, with the inner tube surrounded by insulation or a vacuum. While this multiple concentric tube design reduces the xe2x80x9cshort-circuitingxe2x80x9d effect, it is practically difficult to build and could be functionally cost-prohibitive.
The problem encountered with insulating the heat transfer return line, by means of fully surrounding a portion of same with insulation as per Kuriowa, or by means of a fully insulated concentric tube within a tube as per Dressler, or by means of a fully insulated return line as per Wiggs"" predecessor designs, is that the fully insulated portion of the return line is not exposed to naturally occurring geothermal temperatures, and is therefore a costly necessary underground/underwater system component which is not capable of being utilized for geothermal heat transfer purposes. While the utilization of such fully insulated costly components is an improvement over prior totally un-insulated geothermal heat transfer line designs subject to a xe2x80x9cshort-circuitingxe2x80x9d of the maximum heat gain/loss potential, a design which insulates the supply line from the return line and still permits both lines to retain natural geothermal heat exchange exposure would be preferable, as disclosed in U.S. patent application Ser. No. 10/127,517 by Wiggs. Further, of course, even in horizontal and vertical closed-loop water-source heat pump systems, this xe2x80x9cshort-circuitingxe2x80x9d effect, caused by the supply and return water transfer lines being in close proximity to one another, is a problem which deters from operational system efficiencies.
An additional problem encountered with traditional closed-loop water-source systems is the fact that, traditionally, xc2xe inch to 2 inch diameter plastic water transfer tubing is utilized, so as to reduce plastic pipe costs and excavation/drilling expenses. However, as a general principle, smaller pipe sizes have greater friction efficiency losses, which result in increased requisite pumping energy.
In the early 1990s, Wiggs developed the proposition of excavating a large surface, and near-surface, area of land for the placement of a sealed container, filled with a heat conductive liquid, such as water or water and anti-freeze, and then permanently placing the exterior heat exchange tubes of a direct expansion system into the liquid-filled container. However, after a more detailed review and confidential discussion with others, it was determined that the cost, as well as the requisite surface land area requirements, involved were not likely to be advantageous over a conventional direct expansion exterior heat exchange tube installation design, so the proposition was abandoned by Wiggs. Further, such an installation would still be affected by near-surface temperature fluctuations in both the summer and the winter, and would still be subjected to xe2x80x9cshort circuitingxe2x80x9d efficiency disadvantages encountered by a mixture of heated and cooled container liquid. The present invention, however, is superior to Wiggs"" former proposition in that via the subject invention, deep sub-surface temperatures are accessed which are relatively stable year round; surface area requirements to install the system are minimal, avoiding the necessity of tearing up a yard or a pavement area; and the otherwise necessary extensive excavation and soil removal costs are replaced by a simple drilling expense. Further, and importantly, the xe2x80x9cshort circuitingxe2x80x9d disadvantages are avoided.
Finally, while discussions have been entertained regarding the desirability of incorporating solar heating benefits into a geothermal heating system, as well as incorporating evaporative cooling benefits into a geothermal cooling system, there have been practical obstacles, such as potential extreme system operational pressure differentials, flash gas problems, system short-cycling, and energy storage issues.
Although potentially unnecessary in a sub-surface application where the sub-surface conditions include a substantial amount of natural water convection, such as in a lake, ocean, or aquifer, where the Thermally Exposed Centrally Insulated Geothermal Heat Exchange Unit disclosed by Wiggs in U.S. patent application Ser. No. 10/127,517 would be appropriate, a system design for geothermal direct expansion heat pumps, and/or for geothermal water-source heat pumps, which better avoided xe2x80x9cshort-circuitingxe2x80x9d problems, which decreased friction efficiency losses, and which enabled solar heating and/or evaporative cooling supplements to be effectively utilized, with minimal additional costs, in subterranean soil and/or rock and/or stagnate water conditions, would be preferable. Such a preferable system would also be utilized in conditions containing a substantial amount of natural water convection where it would be useful to isolate the liquid coming into direct contact with copper refrigerant tubing from the surrounding natural water conditions, such as when the natural surrounding water conditions contain significant amounts of sulfur, acid, chlorine, or other substance potentially harmful to copper refrigerant tubing.
It is an object of the present invention to further enhance and improve the efficiency and installation cost functionality of predecessor geothermal heat exchange designs. This is accomplished by means of a sealed casement within a deep borehole, within which a fully insulated open-ended pipe is placed from the top of the casement to a point near the bottom, with the top of the pipe extended to a sealed and fully insulated liquid container within which copper, or other suitable material, refrigerant transport heat transfer tubing is placed. The copper refrigerant tubing extends, by means of a supply and a return line, to and from a compressor, an interior air handler, and related conventional heat pump equipment, without the necessity for a defrost cycle. The container is attached to the casement and to the pipe so as to permit heat conductive liquid circulation from the bottom of the casement, through the pipe, around the copper refrigerant tubes, and back down the casement, which casement is in direct thermal contact with the surrounding sub-surface earth. Circulation of the heat conductive liquid, such as water or water and anti-freeze, is effected by a liquid pump situated within the top of the pipe. A conventional solar heat collector system is connected to the container, which provides a heat sink for the solar system in the winter, and which provides supplemental heat to the primary geothermal system. The supply refrigerant vapor line runs through a condensate water collector in the summer, before the line enters the container, to provide supplemental evaporative cooling.
More specifically, a borehole is drilled to a specified depth, depending on the amount of heat transfer desired, and a casement, such as a six inch diameter steel or plastic casement, which casement has been sealed at the bottom and at all joint areas along the sides, is inserted into the full depth of the borehole. Next, a smaller diameter, such as a two and one-half inch diameter open-ended plastic pipe, which has been fully insulated, is inserted to a depth near, within about six to twelve inches, the bottom of the sealed casement. The sealed primary casement extends to a point near, or above, the surface where the open-ended plastic pipe connects to a sealed container, such as a plastic tub. The plastic tub and the primary casement are fully insulated above-ground and to a depth at least equal to the maximum frost/heat line. Heat exchange coils, such as copper refrigerant tubing, having sufficient surface area to transfer the desired amount of heat, are placed into the sealed container, with an insulated supply and return refrigerant line extending to a conventional heat pump system, comprised of a compressor, an expansion valve, an interior air handler, and other customary equipment well-known to those in the trade. The sealed container, casement, and open-ended pipe are all then filled with a heat transfer liquid, such as water and/or water and anti-freeze, and a liquid circulating pump is attached near the top of the pipe so as to pull liquid up through the open-ended pipe from the bottom of the casement deep underground. As the liquid from the bottom of the casement is pulled up through the insulated pipe, the liquid from the bottom of the casement, which is cool in the summer and warm in the winter, will circulate over the refrigerant heat transfer line, which are hot in the summer and cold in the winter, and the liquid will be pulled back to the bottom of the casement, where heat supplied to, or taken from, the liquid, through the walls of the copper refrigerant heat transfer line by the circulating refrigerant, will be transferred to the surrounding geothermal soil and/or rock and/or water by means of natural heat convection as the liquid travels to the bottom of the casement. Since the central pipe diameter is relatively large, and since the diameter of the casement is larger than the pipe, frictional efficiency losses will be minimized and efficiencies significantly increased. Further, since the pipe inside the casement is fully insulated, the common xe2x80x9cshort circuitingxe2x80x9d heat transfer effect between the supply and return liquid lines will be substantially eliminated.
The subject invention also discloses a means of providing the warmest water from the bottom of the casement to the exiting portion of the refrigerant traveling to the compressor in the winter, as well as a means of providing the coolest water from the bottom of the casement to the exiting portion of the refrigerant traveling to the interior air handler in the summer, by means of an arrangement of piping and solenoid and/or check valves designed to switch liquid flow direction into and out of the container in a fashion commensurate with the desired refrigerant flow direction in either of the heat pump system""s operational heating or cooling modes. Also, a diffuser is incorporated at the entering/exiting portion of the liquid supply/return tubes within the container so as to provide relatively even heat distribution along the refrigerant heat exchange line(s) within the container. This will enhance system efficiencies, as well as help to ensure that the warmest sensible air is provided to the interior conditioned air space in the winter, and that the coolest sensible air is provided in the summer.
As an optional efficiency enhancing supplement, solar heating may be utilized with the system in the winter. A conventional solar heating apparatus is connected in a manner so as to place the solar system""s heat sink exchanger within the sealed and fully insulated liquid container. The intense heat from the solar collector will be diluted via the liquid within the container, thereby preventing operational refrigerant pressure extremes. The solar heat sink can be located at any desired point within the container, close to, or away from, the liquid supply line, so as to provide more, or less, solar heat supplement effect directly to the refrigerant fluid circulating within the refrigerant tubing as desired via preferred system operational refrigerant pressures. Any supplemental solar heat not initially absorbed by the refrigerant fluid within the refrigerant tubing will be absorbed by the liquid circulating down the casement, where the surrounding cooler earth will absorb the extra heat, and will act as a heat storage bank for a relatively continuous supplemental heat supply during the night or cloudy days. The solar heating system is enacted by a heat sensor set to engage the solar heater liquid pump when the solar heating system is able to provide heated liquid at a temperature which exceeds the temperature of the available subterranean geothermal heat.
Another type of optional efficiency enhancing solar heating supplement may be utilized with the system in the winter. In this secondary type of solar heating supplement, the solar heat collector would necessarily be located at an elevation below the solar heat sink lines within the container. This secondary type of solar heating would operate in the same manner as the first type described above, with an adjustable solar heat sink location within the container, and with any extra heat being absorbed by the liquid in the container circulating down the casement, except that the solar heating system would operate by means of refrigerant-filled supply and return refrigerant transport lines without the necessity for a liquid pump. The sun would heat the refrigerant fluid in the solar heat collector, vaporizing the refrigerant. The vapor would naturally rise into the solar heat sink tubes within the fluid within the container. The cooler liquid within the container would absorb the heat from the solar heated refrigerant. With the solar heated refrigerant vapor""s heat removed by the fluid in the container, the refrigerant would condense back into a liquid, which liquid would be pulled by gravity back down into the solar heat collector, where the process would be continuously repeated until the solar collector was no longer able to supply a greater amount of heat than the sub-surface geothermal heat exchanger, at which point the solar heat collector would be disengaged by means of a heat sensor""s signal to close operative solenoid valves, or the like.
A solar heat collector typically requires a minimal amount of electrical energy to operate. Since the solar system""s liquid pump will require only a minimal amount of energy to circulate liquid within the pipe and casement, a conventional solar cell/storage battery system, or other renewable energy source, can be utilized to provide this total power requirement. Further, since the compressor unit""s power draw for this unique system design will be so low, with a 3 ton system periodically operating on as little as 1.5 kw, the solar cell/battery storage system, or other renewable energy source system such as wind or water, could be enlarged to provide the total system energy requirement.
In the summer, a portion of the outdoors hot gas refrigerant vapor line is immersed in, or channeled through, the condensate water produced by the interior air handler in a manner so as to facilitate evaporative cooling. The condensate water can preferably be gravity fed, or can be directed to the desired location via a conventional condensate water pump, which condensate pump could also be powered by a solar cell system. This optional evaporative cooling segment will serve to take away the most extreme heat prior to the refrigerant entering the container, thereby reducing the cooling load requirements of the subterranean casement.
Except for the optional evaporative cooling segment, insulating material, such as styrofoam or rubatex, is placed around all exposed above-ground system components, and around all sub-surface exposed system components to a point at or slightly beyond the maximum frost line or significant heat line, whichever point is greater. The liquid supply pipe extending to almost the bottom of the casement is fully insulated to prevent a xe2x80x9cshort circuitingxe2x80x9d effect with the surrounding return liquid from the container. Additionally, all other out-of-liquid refrigerant and liquid transport lines, except for the evaporative cooling segment, should be fully insulated.
When using direct expansion or other heat pump interior equipment with minimal elevation and distance differentials, an oil separator would be unnecessary, although other customary direct expansion or other refrigerant system apparatus and materials would generally be utilized, including a receiver, thermal expansion valves, an accumulator, and an air-handler, for example as described in U.S. Pat. No. 5,946,928 to Wiggs, all of which are well-known to those in the trade. If one elected to use conventional air source heat pump equipment, well known to those in the trade, in conjunction with the present invention, which invention would replace the air-source system""s exterior fan/coil unit, the air-source system""s defrost cycle function must be by-passed or removed.
The subject invention may be utilized as an individual unit, or by means of multiple units connected by tubing in series or in parallel, to increase operational efficiencies and/or to reduce installation costs in a number of applications, such as in, or as a supplement to, a conventional geothermal direct expansion heat pump system and/or a conventional geothermal closed-loop water-source heat pump system, or as a supplement to a conventional air-source heat pump system. The invention may be utilized to assist in efficiently heating or cooling air by means of a forced air heating/cooling system, or to assist in efficiently heating or cooling a liquid, such as water, in a hydronic heating/cooling system. Additionally, the subject invention may be utilized as a heating or cooling source in a mechanical and/or any other system.